ES2626430T3 - Braking system for a vehicle - Google Patents

Abstract

Braking system for a vehicle with a main brake cylinder (10), with a floating piston of the main brake cylinder that can be at least partially adjusted in the main brake cylinder (10); a brake fluid accumulation device (12, 20) into which a predetermined accumulation volume of a brake fluid can be transferred, wherein the brake fluid accumulation device (12, 20) is a reservoir of brake fluid brakes (12) or a low pressure accumulation chamber (20); a first valve (18) closed without current, which is hydraulically connected to the main brake cylinder (10) by means of a first supply line (44), and by means of which the brake fluid accumulation device (12, 20 ) is hydraulically connected to the main brake cylinder (10), so that in the case of a setting of the floating piston partially inside the main brake cylinder (10) on an adjustment stroke below a corresponding limit adjustment stroke To the accumulation volume, a volume of brake fluid that is less than the predetermined accumulation volume can be transferred from the main brake cylinder (10) to the brake fluid accumulation device (12, 20) via the first valve (18) at least partially open; a first brake circuit (26) with two wheel brake cylinders (32a, 32b) and in each case a wheel intake valve (54a, 54b) and in each case a wheel discharge valve (42a , 42b) per wheel brake cylinder (32a, 32b), where each of the two wheel intake valves (54a, 54b) and the two wheel discharge valves (42a, 42b) of the first brake circuit (26) has two connections and in each case is a valve that can be continuously adjusted; a second valve (30) open without current, which, through a branch point (48) in the first supply line (44) is hydraulically connected with the main brake cylinder (10) and by means of which the first circuit (26) is hydraulically connected to the main brake cylinder (10), so that by means of the second closed valve (30) a pressure increase in the two wheel brake cylinders (32a, 32b) of the wheel can be prevented. first brake circuit (26) in the event of an increase in pressure in the main brake cylinder (10), and by means of the second valve (30) closed at least partially, a pressure increase in the two brake cylinders of the wheel (32a, 32b) of the first brake circuit (26) can be transferred in the event of pressure increase in the main brake cylinder (10); a second brake circuit (28) with two wheel brake cylinders (86a, 86b), a switching valve (96), a high-pressure selector valve (90), and in each case an intake valve of the wheel (108a, 108b) and in each case one wheel discharge valve (120a, 120b) per wheel brake cylinder (86a, 86b), where each of the two wheel intake valves (54a, 54b) of the second brake circuit (28) has two connections and in each case is a valve that can be continuously adjusted, and each of the two discharge valves of the wheel (42a, 42b) of the second brake circuit ( 28) has two connections and in each case is a selector valve, where the second brake circuit (28), by means of a second supply line (88) that leads to the high pressure selector valve (90), is hydraulically connected to the main brake cylinder (10), and where the switching valve (96), through a branch point (92) formed in the second supply line (88), it is also hydraulically connected with the main brake cylinder (10); and a control device (34), by means of which each of the two wheel intake valves (54a, 54b) and the two wheel discharge valves (42a, 42b) of the first brake circuit can be controlled (26), each of the two wheel intake valves (54a, 54b) and of the two wheel discharge valves (42a, 42b) of the second brake circuit (28), the switching valve (96 ) and the high pressure selector valve (96), and additionally the first valve (18) and the second valve (30) can be switched in opposition, so that through a control of the first valve (18) in its state open and of the second valve (30) in its closed state the braking system can be controlled in a first mode, where a pressure increase in the main brake cylinder (10) is prevented in the case of adjusting the floating piston of the main brake cylinder partially into the main brake cylinder (10) in the adjustment stroke below of the limit setting travel, and through a control of the first valve (18) in its closed state and of the second valve (30) in its open state the braking system can be controlled in a second mode, where an increase in The pressure in the main brake cylinder (10) is ensured by adjusting the floating piston of the main brake cylinder, partially in the main brake cylinder (10), on the setting stroke below the limit setting stroke, characterized in that By controlling the first valve (18) in its open state and the second valve (30) in its closed state, an intervention of the main brake cylinder (10) on the two wheel brake cylinders ( 32a, 32b) of the first brake circuit (26) and a pressure increase in the two wheel brake cylinders (32a, 32b) of the first brake circuit (26) despite a pressure increase in the brake cylinder. main brake due to second valve (30) closed; through the control of the first valve (18) in its closed state and of the second valve (30) in its open state a pressure increase in the main brake cylinder (10), by means of the second valve (30) at least partially open, it can be transmitted to the two wheel brake cylinders (32a, 32b) of the first brake circuit (26); and the braking system has exactly twelve valves that can be activated (18, 30, 42a, 42b, 54a, 54b, 90, 96, 108a, 108b, 120a, 120b) as the first valve (18), the second valve ( 30), the two wheel intake valves (54a, 54b) and the two wheel relief valves (42a, 42b) of the first brake circuit (26), the two wheel intake valves (54a, 54b) and the two relief valves (42a, 42b) of the second brake circuit (28), the switching valve (96) and the high-pressure selector valve (90), which can be controlled at least in their open state and in its closed state by at least one electrical control signal (36) provided by the control device (34), where the first valve (18) in its open state and the second valve (30) in its closed state can be switched as opposed by a common current signal of the control device (34) as a control signal (36).

Description

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DESCRIPTION

Braking system for a vehicle

The present invention refers to a braking system for a vehicle.

State of the art

The electric vehicles and hybrid vehicles have a braking system designed for recovery braking, with an electric motor operated rheostatically during recovery braking. The electric energy obtained during the recovery braking, after an intermediate storage, is preferably used for vehicle oil. In this way, an energy dissipation, an energy consumption and an emission of harmful substances from the electric or hybrid vehicle can be reduced, which occur during a runaway in the case of frequent braking.

However, the rheostatic operation of the electric motor, for example of the electric drive motor, generally presupposes a certain minimum speed of the vehicle. Thus, a recovery braking system is often not in a position to exert a rheostatic braking torque on the wheels of the vehicle until the vehicle, previously in decommissioning, is in a state of detention. Therefore, a hybrid vehicle, additionally with respect to the rheostatically operated electric motor, often presents a hydraulic braking system, by means of which, at least in a reduced speed range, the braking effect can be compensated which is removed from the recovery brake. In that case, also in an electric energy accumulator, when the brake of recovery generally does not exert any braking torque on the wheels, the braking torque in its totality can be applied by means of the hydraulic braking system. On the other hand, in some situations it is considered desirable to exert on the wheels a hydraulic braking force io as small as possible, to achieve a high degree of recovery. As an example, after the change processes, the uncoupled generator is frequently activated as a recovery brake to guarantee a reliable charge of the intermediate accumulator and a high energy saving.

Generally, a driver prefers a totai braking torque of his vehicle that corresponds to his activation of a brake actuation element, as for example his activation of the brake pedal, regardless of an activation or deactivation of the recovery brake. Some electric vehicles and hybrid vehicles presently have an automatic system that should fulfill the function of the deceleration regulator and that must adapt the braking torque of the hydraulic braking system to the current braking torque of the recovery brake, so as to maintain a totai braking torque desired. Examples of an automatic system of that class are ios brake by wire braking systems, in particular the EHB systems. However, due to their expensive electrical, mechanical and hydraulic units, the electric brake systems are really expensive.

As an alternative with respect to the electric brake systems, in the so-called DE 10 2008 002 345 A1 a braking system is described which comprises a first brake circuit uncoupled from a main brake cylinder and connected to a liquid storage tank. brakes. A wheel axle is associated with that first brake circuit, on which one can use a recovery braking torque of a rheostatically operated electric motor. In this way, two other brake circuits are fitted to the main brake cylinder, so that the driver can brake directly on them, thus exerting a pair of hydraulic braking on the wheels associated with the other brake circuits. In addition, the braking system has a certain pedaling path.

In the application WO 98/31576 A1 a first braking system is described with more than two vans that can be operated electrically. A second braking system of the soiicity WO 98/31576 A1 has twelve wrenches that can be activated electrically and two proportional pressure wrenches. In the application JP 11 285102 A, a braking apparatus for an electric vehicle is described without precise information on the quantity of the vans that can be activated electrically, of the respective braking apparatus. The so-called WO 2008/155045 A1 soio describes braking systems with more than twelve units that can be activated electrically. The brake systems of the soicity JP 2002 255018 A have all two identical brake circuits. In the application of DE 43 22 182 A1, the number of valuations of the braking systems described is not indicated. In the application of DE 10 2009 007 494 A1, several electrically controlled braking systems with a simulator function are described, where none of the braking systems however has a brake circuit with a switching valuation and a sewing of a pressure pressure . In the braking system described in the application WO 2010/102844 A1, a brake fluid clearance from the main brake cylinder to a brake fluid tank is only possible by means of a separation gap, even if at least one other delay The same brake circuit is controlled in its open state. The aforementioned also applies to the hydraulic braking system for motor vehicles of the type WO 03/053755 A1. Likewise, the application of DE 196 04 134 A1 describes a suppression of a braking torque of the generator by means of at least one wheel discharge discharge of its braking system.

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Description of the invention

The present invention creates a braking system for a vehicle with the characteristics of revindication 1. Advantages of the invention

The invention enables a braking system, in which the idle travel of the braking actuation element (for example the idle travel of the pedal) can be predetermined in a variable manner by the electrical activation of the first valve. As long as the first valve is in an open state, the idle travel of the braking actuator element has at least the length of the adjustment travel limit. On the other hand, in the case of a first closed valve, the driver already during an adjustment of the floating piston of the main brake cylinder in an adjustment path below the adjustment path shall, that is, in the case of a corresponding minimum drive of the brake actuating element, it can brake directly on the main brake cylinder, thereby causing an increase in pressure on the main brake cylinder.

The braking system according to the invention is characterized by a variable and / or suppressive vacuum path of the braking drive element. Thus, in the present invention it is possible to take advantage of an idle travel of the braking drive element to increase efficiency in the case of a recovery, while eliminating the disadvantages of an extended idle travel of the brake element. braking drive at the hydraulic safety level.

The aforementioned can also be described so that, in the present invention, the idle travel of the braking drive element can be optionally regulated. As long as the first valve is open, the braking actuation element disposed in the main brake cylinder has an empty path whose length corresponds at least to the limit adjustment path. On the other hand, after a closure of the first valve, already an actuation of the braking actuation element in an actuation path within the optionally adjustable vacuum path can cause a pressure constitution in the main brake cylinder.

The brake fluid accumulation device is designed so that at least a predetermined accumulation volume can be transferred without back pressure, that is, with a non-significant force. The adjustment path of the floating piston of the main brake cylinder corresponds to a volume of the brake fluid which, in the case of an adjustment without the pressure constitution of the floating piston of the main brake cylinder, is partially displaced towards the cylinder of main brake in the adjustment path llmite, from the main brake cylinder. The mentioned displaced volume, preferably, is equal to the accumulation volume of the brake fluid accumulation device. This can also be described as a correlation between the limit adjustment path and the predetermined accumulation volume.

The idle travel of the braking drive element linked to the main brake cylinder, thus, advantageously, can be adjusted to a preferred length for the current situation of the vehicle and / or the current situation of the environment.

In addition, the braking system comprises a control device, designed so that by means of the control device, through a control of the first valve in its open state and the second valve in its closed state, the braking system can controlled in a first mode, where an increase in pressure in the main brake cylinder is prevented in the case of adjusting the floating piston of the main brake cylinder partially in the main brake cylinder in the adjustment travel below the travel path of adjustment limits, and through a control of the first valve in its closed state and of the second valve in its open state the braking system can be controlled in a second mode, where an increase in pressure in the main brake cylinder is guaranteed by adjusting the floating piston of the main brake cylinder, partially in the main brake cylinder, in the adjustment travel below the adjustment travel limit . Thus, the braking system controlled in the first mode has a minimum vacuum path that preferably approaches zero. On the other hand, the braking system controlled in the second mode has an idle path that corresponds at least to the limit adjustment path. With this, the advantage of a variable vacuum path and / or that can be suppressed from the braking drive element can be realized simply.

The brake fluid accumulation device is a brake fluid reservoir or a low pressure accumulation chamber. Thus, for the brake fluid accumulation device a component can be used that is usually already in the braking system and / or an additional component convenient in terms of costs. Additionally, such a conformation of the brake fluid accumulation device does not increase the need for braking system space or only minimally increases it.

The invention also makes it possible to disengage the first brake circuit, without the need for a simulator or a certain empty path (pedal travel) in the braking system. Of this

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mode, the advantageous embodiment is compatible / can be applied in preferred types of hydraulic braking systems. It is not necessary to suppress the simulator at the hydraulic safety level expensively when removing a simulator or a certain vacuum path in the braking system. In the same way, the driver must not overcome a vacuum travel to be able to brake directly on the main brake cylinder, as well as at least one brake circuit fixed on the main brake cylinder. At the same time, by means of the second valve, the first brake circuit, which for example is associated with an axle of the vehicle, can be disengaged for an effective use of the recovery.

The closed running without power of the first valve is associated with the advantage that, in the case of a malfunction and / or a failure of the electronic unit of the braking system, the vacuum travel is automatically reduced to a minimum . Preferably, the empty path is then reduced to approximately zero, which can also be expressed as "suppression" of the empty path. The open running without power of the second valve guarantees the additional advantage that the driver, in the event of a malfunction and / or a failure of the electronic unit of the braking system without a vacuum travel, can brake directly at least in the first brake circuit. In this way, in a simple way, and with an inversion of forces that can be easily applied, the driver can brake even safely in such a situation.

By means of the control device, the first and second valves can be switched in opposition to phases. As a switching in opposition to phases of the first valve and the second valve it is understood that the second valve closes automatically in case of opening the first valve and that the second valve opens automatically in case of a closing of the first valve. This advantageous switching in opposition to phases of the first valve and the second valve, in the advantageous execution of the two valves in the preceding paragraph, can be conveniently carried out in terms of costs through a current application in common with A current signal. In an advantageous development, the first brake circuit comprises a pump, by means of which another volume of brake fluid can be pumped from a brake fluid reservoir, into the two brake cylinders of the wheel of the first brake circuit. Thus, after a closure of the second valve, by pumping the volume of brake fluid from the brake fluid reservoir to the two brake cylinders of the wheel of the first brake circuit, there is the possibility of constituting / Actively regulate a hydraulic braking torque exerted on at least one associated wheel, by the wheel brake cylinders. Also after a disengagement of the first brake circuit from the main brake cylinder, a braking of the associated wheels can be caused by a pump drive. In particular, by pumping the other volume of brake fluid into the brake cylinders of the wheel, a temporary decrease of a braking torque of the generator can be compensated during the suppression. In addition, the braking system may comprise an overpressure valve disposed between a pumping side of the pump and the brake fluid reservoir. In that case, the pump with at least one other pump of the braking system can be arranged on a common shaft of an engine, without a joint drive of the pump with at least one other pump leading to an unwanted pressure / overpressure constitution in the First brake circuit. Instead, in such a situation, by opening the overpressure valve, the volume pumped by the pump is transferred to the brake fluid reservoir. Thus, the braking system equipment with another motor is not necessary for at least two pumps. The braking system has precisely twelve valves that can be activated, by means of which at least one electrical signal provided by the control device can be controlled at least in an open state and in a closed state. For a braking system of that kind, a convenient cost-control device can be used.

According to the invention, the braking system comprises a second brake circuit with two wheel brake cylinders that are hydraulically connected to the main brake cylinder by means of a switching valve and a main selector valve. The two brake circuits can be used in the braking system to brake in the case of an unmodified braking sensation during the actuation of the braking drive element instead of on both axles of the vehicle, optionally, on a first axle associated with the first brake circuit, or on a second axis associated with the second brake circuit, thereby maximizing the recovery efficiency of the braking system. In particular, by closing the first valve a sufficiently long path can be regulated and, during a drive of the braking actuator element in an actuation path within the vacuum path, it can be braked with the first disengaged brake circuit of the cylinder. main brake, while in the second brake circuit there is no increase in pressure. This facilitates recovery in a braking system, enabling advantageous driving comfort in the event of a suppression. It should be noted once again that the advantages described in the preceding paragraphs are realized in a braking system that does not have a vacuum path through a space formed between the braking drive element and the floating piston of the main brake cylinder. This eliminates the disadvantages of such a space, such as the need for a simulator to artificially generate a braking sensation before the space is closed and / or the driver's additional drive to close the space. The present invention makes possible in particular a suppression of a braking torque of the generator, without the driver having to execute an additional work force. At least one hydraulic braking torque of at least one wheel brake cylinder of the first brake circuit can be adjusted

(actively) after a decoupling of the main brake cylinder, so that a temporarily variable generator braking torque is suppressed, as well as so as to maintain a total advantageous / preferential deceleration of the vehicle, for example corresponding to the actuation of the element of brake actuation through the driver and / or a predetermination of an automatic speed control unit, despite the temporarily variable generator braking torque. This ensures a suppression process that has no effect on the braking path. The present invention thus offers a convenient alternative in terms of costs compared to a traditional electric cable braking system, which is considered very advantageous for vehicles with rear-wheel drive or all-wheel drive. However, the invention can also be applied to the front drive with a front axle by electric cable.

10 However, the present invention is not limited to an application in an electric or hybrid vehicle. For example, a distribution of the braking force that depends on the transverse acceleration can also be carried out by the present invention. In the case of a distribution of the braking force that depends on the transverse acceleration the braking force is divided into some wheels of the vehicle, preferably on the two wheels of the rear axle, in correspondence with a tread force that occurs when traveling In a curve. In this way, the friction coefficient of the wheels, first of all the friction coefficient of the two rear wheels, can be adapted to the transverse acceleration. In this way, the vehicle brakes more stable in the curves. Preferably, in order to determine at least one hydraulic braking torque that must be actively regulated, a transverse acceleration determined by a sensor device is used.

Additionally, a use of the present invention is possible for dynamic braking. In dynamic braking of curves, the braking force on an internal wheel of the curve is increased compared to the braking force on an external wheel of the curve. This achieves a more dynamic driving behavior.

The invention can also be used for more advantageous braking during a reverse movement. In particular, through an increase in the braking force on the rear axle, an improved braking force distribution is regulated, for a reverse movement. There is also talk of a distribution of rear gear. Mainly in a slow movement in reverse running downhill this allows a markedly more stable driving behavior.

Notwithstanding the possibility of an active regulation of at least the (second) hydraulic braking torque exerted by the second brake cylinder of the wheel, the driver, after a switching of the braking system in the first 30 operating mode, can brake directly on the second wheel brake cylinder. In this way, the driver can easily execute sudden braking processes.

Brief description of the drawings

Other features and advantages of the present invention are explained below by the figures. The figures show:

35 Figure 1: a circuit diagram of a first embodiment of the braking system;

Figure 2: a circuit diagram of a second embodiment of the braking system;

Figures 3 and 4: respectively a circuit diagram of a third and fourth ways of executing the braking system and;

Figure 5: A flow chart to represent a procedure that is not considered within the present invention.

Forms of Execution of the Invention

The braking systems represented schematically in the following figures can not only be applied in an electric or hybrid vehicle. Instead, each of the mentioned braking systems can, for example, also be used for a preferential distribution of the braking force on the wheels of the vehicle, in the case of braking during a movement in a curve and / or during a shift in reverse. The indications described below on the possibility of using the braking systems in an electric or hybrid vehicle should be understood by way of example only.

Figure 1 shows a circuit diagram of a first embodiment of the braking system.

The braking system comprises a main brake cylinder 10 and an additional brake fluid reservoir 12. At 50 the main brake cylinder 10 is arranged a floating piston of the main brake cylinder (not shown) which

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it can be adjusted inwards at least partially. The brake fluid reservoir 12 should not be understood as the main brake cylinder 10. Instead, as the brake fluid reservoir 12 can be understood a volume of brake fluid or a brake fluid container, whose internal pressure it can be regulated independently of an internal pressure of the main brake cylinder 10 or corresponds to a predetermined fixed pressure, such as atmospheric pressure. In this way, the brake fluid reservoir 12 can also be referred to as a brake fluid accumulation device, to which a predetermined accumulation volume of the brake fluid of the main brake cylinder can be transferred without back pressure. Between the main brake cylinder 10 and the brake fluid reservoir 12, a perforation can be made for the change of brake fluid, such as a breathing opening. However, the main brake cylinder 10 and the brake fluid reservoir 12 can also be made without a hydraulic connection.

A brake actuator element 14, such as a brake pedal, can be arranged in the main brake cylinder 10. As an alternative or in a complementary way with respect to a brake pedal, a braking actuation element 14, which is made in another way, can also be used. By driving the braking drive element 14, a driver of a vehicle equipped with the braking system can cause an increase in pressure in an internal volume of the main brake cylinder 10. Preferably, a brake booster 16 is also arranged in the main brake cylinder 10, so that an increase in pressure in the internal volume of the main brake cylinder 10 can also be caused by the brake booster 16. The brake booster 16 can also be for example a pneumatic, hydraulic and / or a brake booster electromechanical brake booster. It should be noted that the possibility of performance of the brake booster 16 is not limited, however, to the examples mentioned herein.

Optionally, a sensor 17 may also be arranged in the braking drive element 14, so that a drive of the braking element 14 can be registered by the driver by the sensor 17. Preferably, the sensor 17 is designed to provide a signal of the braking force and / or the braking distance corresponding to the actuation of the braking actuation element 14, to an electronic evaluation unit / electronic control unit (not shown). The possibility of using the information that can be provided by the sensor 17 will not be discussed in detail. Conveniently in terms of costs, the sensor 17 may be a sub-unit of the brake booster 16. Similarly, the sensor 17 may be a pedal travel sensor, an amplifier membrane distance sensor and / or a bar distance sensor. However, the possibilities of executing the sensor 17 are not limited to the examples mentioned here.

The braking system has a first valve 18 that can be controlled electrically, by means of which an accumulation chamber 20 is hydraulically connected to the main brake cylinder 10. The hydraulic connection between the accumulation chamber 20 and the main brake cylinder 10 is performed so that in the case of an adjustment of the floating piston of the main brake cylinder partially inward of the main brake cylinder 10 in an adjustment path under a predetermined adjustment path, a volume of brake fluid can be transferred without back pressure from the main brake cylinder 10, by means of the first valve 18 open (at least partially), towards the accumulation chamber 20. This can be guaranteed, since the accumulation chamber 20 is made as a liquid accumulation device of brakes, to which a predetermined volume of brake fluid can be transferred, without cont rappression The default setting adjustment path corresponds to the default accumulation volume. This can also be expressed so that a volume equal to the accumulation volume of the accumulation chamber 20, in the case of an adjustment into the floating piston of the main brake cylinder is displaced from the main brake cylinder 10 while maintaining an internal pressure main brake cylinder constant. By opening (at least partially) the first valve 18 can thus be prevented! A pressure constitution during the inward adjustment of the floating piston of the main brake cylinder in an adjustment travel of at least the adjustment travel is limited. The advantages that result from it are described in detail below.

The accumulation chamber 20 can be for example a low pressure accumulation chamber. For the first valve 18 a separating valve / selector valve can be used that can only be controlled electrically in an open mode and in a closed mode. In parallel with respect to the first valve 18, preferably, a bypass line 22 is made with a retention valve 24 that prevents a displacement of brake fluid by the bypass line 22, from the main brake cylinder 10 towards the accumulation chamber 20.

The braking system can be controlled through an (at least partial) opening of the first valve 18 in one way, where an increase in pressure in the main brake cylinder 10 is prevented in the case of an adjustment into the Floating piston of the main brake cylinder in the adjustment path below the limit adjustment path. This can also be expressed in such a way that the braking system controlled in the first mode has an "idle travel" corresponding to the limit adjustment travel. As long as the first valve 18 is open (at least partially), the braking drive element 14 can be adjusted in a drive path to the "idle path", without the adjustment of the floating piston of the brake cylinder

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main in the adjustment path to the adjustment path will cause an increase in pressure in the main brake cylinder. That "idle travel" made in the first mode does not require a space that must be overcome / closed between a first contact piece of the braking drive element 14 and a second contact piece of the floating piston of the main brake cylinder.

Additionally, the braking system can be controlled through a closure of the first valve 18 in a second mode, where an increase in pressure in the main brake cylinder 10 can be caused in the case of an adjustment into the Floating piston of the main brake cylinder in the adjustment path below the limit adjustment path. After a control of the braking system in the second mode through the closure of the first valve 18, the driver has the possibility of causing an increase in pressure in the main brake cylinder 10 by actuating the braking drive element 14 in an actuation path below the "idle path" (which can be eliminated / deactivated) The closing of the first valve 18 can be performed faster than the traditional way to be performed for overcoming / closing the "vacuum path" to a constitution of pressure in a main brake cylinder. In addition, that control of the braking system, which can be performed electrically in the second mode, can be performed without the application of force by the driver. As will be described in detail below, the braking system thus suppresses! the disadvantages of a traditional braking system with a vacuum path mechanically realized through a space between a first contact piece of the brake actuating element 14 and a second contact piece of the floating piston of the main brake cylinder.

The first valve 18 and the accumulation chamber 20 are used in this way to carry out a vacuum path that can be modified and / or eliminated. If the first valve 18 is open (at least partially), then the volume of brake fluid can be moved from the main brake cylinder 10 to the accumulation chamber 20, without first creating a pressure constitution in the main brake cylinder 10 and without causing a braking effect. On the other hand, if the first valve 18 is closed, then an actuation of the braking actuation element 14, in the case of a simultaneous simultaneous actuation of the floating piston of the main brake cylinder, directly and preferably without a idle travel mechanically, it can cause a pressure constitution in the main brake cylinder 10, which can activate a braking effect.

The first valve 18 is made as a closed valve without current. In this way, the braking system, in the case of a malfunction and / or a failure of the electronic unit or its power supply, is automatically controlled in the second mode, where already an actuation of the power element. braking drive in a drive path below the "idle path" causes increased pressure in the main brake cylinder 10. In this way, the driver can quickly brake the vehicle in such a situation and / or brake with a reduced strength inversion.

The braking system comprises two brake circuits 26 and 28 that are hydraulically connected to the main brake cylinder 10. The first brake circuit 26 is hydraulically connected to the main brake cylinder 10 by a second valve 30, so that by means of the second valve 30 open (at least partially), an increase in pressure in the main brake cylinder 10 can be transmitted to at least one brake cylinder of the wheel 32a and 32b of the first brake circuit 26. However, if the second valve 30 is in its closed state, an increase in pressure in at least one brake cylinder of the wheel 32a and / or 32b of the first brake circuit 26 can be prevented despite an increase in pressure in the cylinder of main brake 10. Consequently, an intervention of the main brake cylinder is prevented in at least one brake cylinder of the wheel 32a or 32b of the first brake circuit 26, when closed to the second valve 30. Thus, by opening (at least partially) the second valve 30, a hydraulic reaction of at least one brake cylinder of the wheel 32a and / or 32b of the first brake circuit 26 can be guaranteed. as for an increase in pressure in the main brake cylinder 10, while the first brake circuit 26, by closing the second valve 30, can "hydraulically disengage" from the main brake cylinder 30.

In a convenient way of execution in terms of costs, the second valve 30 can be realized as a selector valve / separating valve that can be controlled electrically, which can only be switched to a closed state and in an open state. Alternatively, the second valve can also be a valve that can be regulated continuously / controlled continuously. The second valve 30 is made as an open valve without current. In this way, in the case of a malfunction and / or a failure of the electronic unit of the braking system or of the current supply of the braking system, the driver can still brake safely in the first brake circuit 26.

The braking system comprises a control device 34 schematically represented only partially in its operation, whereby the first valve 18 and the second valve 30 can be switched in opposition to phases. By means of a current application of the valves 18 and 30 with a control signal 36, the first valve 18 closed closed without current is closed, in the case of an opening of the second valve 30 performed openly without current, opening correspondingly in the case of a closure of

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the second valve 30. Thus, for the control device 34 a convenient electronic unit can be used in terms of costs.

In an advantageous embodiment, the first brake circuit 26 is designed so that a brake pressure in at least one brake cylinder of the wheel 32a and / or 32b of the first brake circuit 26, after a closure of the second valve 30, can be constituted / regulated independently of a pressure that is present in the second brake circuit 28 and in the main brake cylinder 10. A suitable execution of the first brake circuit 26 for a braking pressure is described below. which can be actively regulated in two brake cylinders of the wheel 32a and 32b, after the closure of the second valve 30. However, the braking system described herein is not limited to such an execution of the first brake circuit 26 .

In the embodiment shown, the first brake circuit 26 has a first pump 38, whereby a volume can be pumped from the brake fluid reservoir 12 to at least one brake cylinder of the wheel 32a and 32b. Likewise, by means of the first pump 38, a volume can be redirected from the first brake fluid circuit 26 to the brake fluid reservoir 12. To this end, the first brake circuit 26 is connected to the fluid reservoir. brakes 2l via a suction line 40. To control a brake fluid displacement from at least one brake cylinder of the wheel 32a and 32b to the brake fluid reservoir 21, the first brake circuit 26 may comprise at least one valve that can be regulated continuously, by means of which the wheel brake cylinders 32a and 32b are hydraulically connected with the brake fluid reservoir 12. The wheel discharge valves 42a and 42b associated with the brake cylinders of The wheel 32a and 32b are made as valves that can be adjusted continuously. In that case, the active reduction of the braking pressure in the brake cylinders of the wheel 32a and 32b through the movement of the brake fluid to the brake fluid reservoir 12 can be carried out without an additional valve that can be adjusted so continuous, of the first brake circuit 26. The movement of brake fluid from the first brake circuit 26 towards the brake fluid reservoir 40, however, can also be performed without the wheel discharge valves 42a and 42b being made especially as at least one valve that can be adjusted continuously.

An advantageous fixation of the components of the first brake circuit 26 in the main brake cylinder 10 and in the brake fluid reservoir 12 is described below. The first brake circuit 26 is arranged in a first supply line 44, by which the first valve 18, a line 46 leading from the first valve 18 to the accumulation chamber 20 and the accumulation chamber 20, are connected to the main brake cylinder 10. The second valve 30, by means of a branching point 48 on the first supply line 44 and a line 50 leading from it, is hydraulically connected to the main brake cylinder 10. From the second valve 30, a line 52 leads to a first intake valve of the wheel 54a, the which is associated with a first brake cylinder of the wheel 32a of the first brake circuit 26. By means of a branch point 56 arranged in line 52 and a line 58 that continues from and the same, a wheel intake valve 54b associated with the second brake cylinder of the wheel 32b of the first brake circuit 26, is also connected to the second valve 30. Each of the two wheel intake valves 54a and 54b, via a line 60a or 60b, is connected to the corresponding brake cylinder of the wheel 32a and 32b. Parallel with respect to each of the two inlet valves of the wheel 64a and 64b, a bypass line 62a and 62b is extended in each case with a check valve 64a and 64b disposed therein. The check valves 64a and 64b are aligned so as to prevent displacement of brake fluid through the associated bypass line 62a or 62b, from the second valve 30, to the associated brake cylinder of the wheel 32a or 32b .

In each line 60a and 60b a branching point 66a and 66b is made, with which each of the discharge valves of the wheel 42a or 42b is connected by a line 68a or 68b. From each discharge valve of the wheel 42a and 42, a line 70a and 70b leads to a common branch point 72. The branch point 72 is connected to the suction side of the first pump 38 by a line 74. From the side The suction line 40 mentioned above extends from the first pump 38. In the suction line 40 an overpressure valve 76 is placed, the function of which will be described in more detail below. In parallel with respect to the first pump 38 and to the overpressure valve 76, a bypass line 78 is also connected which connects the line 74 with the suction line 40. In addition, the transport side of the first pump 38, via a line 80 , is connected to a branch point 82 made on line 52. Also a first pressure sensor 84 of the first brake circuit 26 is connected to line 52.

The braking circuit, additionally with respect to the first brake circuit 26, also has the second brake circuit 28. The second brake circuit 28 is made such that the brake pressure in at least one brake cylinder of the wheel 86a and 86b of the second brake circuit increases (automatically) with increasing internal pressure in the main brake cylinder 10. The aforementioned can also be described so that the driver, after overcoming the idle path that can be regulated by an opening (at less partial) of the first valve 18 and / or after a removal / deactivation of the empty path through the closure of the first valve 18, it is possible to directly brake at least one brake cylinder of the wheel 86 of the second brake circuit 28. In particular, the second brake circuit 28 may correspond to a

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conventional ESP system. The second brake circuit 28, by means of a second supply line 88 leading to a main selector valve 90 of the second brake circuit 28, is hydraulically connected to the main brake cylinder 10. By a branching point 92 formed in the second supply line 88 and via a line 94 that continues from there, also a switching valve 96 of the second brake circuit 28 is connected to the main brake cylinder 10. In parallel with respect to the switching valve 96, a Bypass line where a check valve 100 is arranged. The check valve 100 is aligned so as to prevent displacement of the brake fluid through the bypass line 98, from a line 102 arranged on the side of the cylinder. brake wheel on switching valve 96, towards line 94. By means of a branch point 104 on the second supply line ion 88, also a second pressure sensor 106 is disposed in the second brake circuit 28.

The line 102 connects the switching valve 96 with a first inlet valve of the wheel 108a which is associated with the first brake cylinder of the wheel 86a of the second brake circuit 28. By means of a branch point 110 formed in the line 102 and a line 112 that continues therefrom, a wheel intake valve 108b associated with the second brake cylinder of the wheel 86b of the second brake circuit 28, is also connected to the switching valve 96. Each of the two wheel intake valves 108a and 108b, in each case via a line 114a or 114b, is connected to the associated brake cylinder of the associated wheel 86a or 86b of the second brake circuit 28. In parallel with respect to the two valves of Admission of the wheel 108a and 108b extends in each case a branch line 116 and 116b with a check valve 118a and 118b. Each of the check valves 118a and 118b is aligned so that a displacement of brake fluid is prevented through the associated bypass line 116a or 116b, from the line 102 to the wheel brake cylinder 86a or Associated 86b. To each of the two brake cylinders of the wheel 86a and 86b of the second brake circuit 28 is also associated a discharge valve of the wheel 120a and 120b, where each, by a line 122a or 122b is connected to a branch point 124a formed on line 114a or with a branch point 124b formed on line 114b. The two wheel discharge valves 120a and 120b, also via a line 126a and 126b, are connected to a common bypass point 128. From the bypass point 128 a line 130 extends towards a suction side of a second pump 132. By means of a branch point 134 formed in line 130 and a line 36, also the main selector valve 90 is connected to the side of transport of the second pump 132. In addition, another accumulation chamber 138, by means of a branching point 140 formed in line 130, is connected to the transport side of the second pump 132. An overpressure valve 142 in line 130 is aligned so that a displacement of brake fluid from the discharge valves of the wheel 120a and 120b to the outlet side of the second pump 132 is only possible in the case of a given pressure. The transport side of the second pump 132, via a line 144, is connected to a branch point 146 made on the line 102.

Preferably, the first pump 38 and the second pump 32 are arranged on a common shaft 148 of an engine 150. The overpressure valve disposed on the suction line, in the case of a joint operation of the first pump 38 with the Second pump 132, guarantees a return transfer of the volume of brake fluid pumped from the brake fluid reservoir 12 by the first pump 38, to the brake fluid reservoir 12, so that there is no overpressure in the first brake circuit 26. As an example, the two inlet valves of the wheel 54a and 54b, when the first pump 38 also operates, are closed when, when the braking pressure is maintained in the first brake circuit 26, the pressure of braking in the second brake circuit should be increased by the second pump 132. In that case, conventionally, between the transport side of the first pump 38 and the intake valves of the wheel 54a and 54b, it often constitutes a higher pressure. Through the advantageous arrangement of the overpressure valve 96, however, the volume transported by the open overpressure valve 76 can be transferred to the brake fluid reservoir 12. In this way damage to the hydraulic unit or an opening can be prevented unwanted valve 54a or 54b.

Due to the advantageous execution of the second brake circuit 28 also in the case of a joint operation of the second pump 132 with the first pump 38 an unwanted pressure constitution is prevented in the second brake circuit 28. In particular through a closure of the main selector valve 90 can ensure that an undesired operation of the second pump 132 causes an unwanted (additional) pressure constitution in the second brake circuit 28.

The first pump 38 and / or the second pump 132 may be a three-piston pump. The braking system described here can be carried out as a six-piston ESP system. Instead of a three-piston pump, however, a pump with another number of pistons, an asymmetric pump and / or a cogwheel pump can also be used as the first pump 38 and / or as the second pump 132.

The braking system shown in Figure 1 has exactly twelve valves that can be activated electrically 18, 30, 42a, 42b, 54a, 54b, 90, 96, 108a, 108b, 120a and 120b, which can be controlled at least in an open state and in a closed state by the control device 34. Due to the amount of

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valves that can be activated, the control device 34 can be conveniently realized in terms of costs. Advantageously, the inlet valves of the wheel 54a, 54b, 108a and 108b and the switching valve 96 are made as open valves without current. However, for the discharge valves of the wheel 42a, 41 b, 120a and 120b and the main selector valve 90 a closed run without current is considered preferred.

The two brake cylinders of the wheel 32a and 32b of the first brake circuit 26 may be associated with the wheels of a first axle of the vehicle, while the two brake cylinders of the wheel 86a and 86b of the second brake circuit 28 are arranged on the wheels of a second axle of the vehicle. Preferably, the brake cylinders of the wheel 32a and 32b of the first brake circuit 26 are associated with the rear axle. In that case it is considered advantageous that a generator (not shown) is also arranged on the rear axle. However, the braking system described here is not limited to a division of the brake circuit in terms of axles. Instead, the braking system can also be used for a vehicle with an X division of the brake circuit.

A particularly advantageous procedure for using the braking system described above is described below, for suppressing a braking torque of the generator. The application capacity of the braking system, however, is not limited to that process.

In a case without braking, that is, when the braking actuation element 14 is not operated, all valves 18, 30, 42a, 42b, 54a, 54b, 90, 96, 108a, 108b, 120a and 120b are without current. In the case of a drive of the braking drive element, the driver (preferably without overcoming a gap between the braking drive element 14 and the floating piston of the main brake cylinder) brakes on the main brake cylinder 10. By means of the sensor 14, ace! as with a corresponding sensor system, the driver's braking desire can be detected immediately. Considering the state of charge of the battery, the current speed of the vehicle, the current situation of the traffic, the conditions detected in the environment, the braking force of the driver, the braking path and / or the speed of the drive of the drive element of braking 14, then it can be determined whether the braking process can be used for a battery charge that is connected to the generator. If the battery charge is not anticipated, the first valve 18 is controlled in the closed state and the second valve 30 is controlled in the open state. The actuation of the braking drive element 14 leads in this case to an increase in the internal pressure in the main brake cylinder and, correspondingly, to an (automatic) increase in the brake pressure in the brake cylinders of the wheel 32a, 32b, 86a and 86b.

As long as the braking process must be used for a charge with the battery connected to the generator, when the driver's braking desire is detected, the first valve 18 opens and the second valve 30 closes. In this way, at least the accumulation volume of the aforementioned brake fluid can be moved without back pressure towards the accumulation chamber 20. A pressure constitution in the main brake cylinder 10 is thereby prevented. Correspondingly, in neither of the two brake circuits 26 and 28 increases the pressure. Instead, the generator can be used to charge the battery without exceeding the maximum deceleration of the vehicle, predetermined by the driver. In this way an identical functionality is realized in comparison with a traditional vacuum path through the formation of a space between the braking actuation element 14 and the floating piston of the main brake cylinder.

In addition, there is the possibility of determining a difference between a desired total braking torque predetermined by the driver by actuating the braking drive element 14 and the generator's braking torque, then actively regulating the braking pressure at the minus one of the brake cylinders of the wheel 32a and 32b disengaged from the main brake cylinder 10, of the first brake circuit, so that the desired total braking torque is maintained. The aforementioned is possible by a corresponding activation of the first pump 38 and / or at least one of the discharge valves of the wheel 42a and 42b. The suppression process, in this way is not perceived or hardly perceived by the driver.

An advantageous activation of the discharge valves of the wheel 42a and 42b of the first brake circuit 26 for the active regulation of the brake pressure in the associated brake cylinders of the wheel 32a and 32b can be carried out so that in the case of a complete closure of one of the two wheel discharge valves 42 a or 42b the regulation of the total brake pressure of the two brake cylinders of the wheel 32a and 32b takes place by means of the other wheel discharge valve 42a or 42b (not closed). In particular to remove the brake, at least one of the two discharge valves of the wheel 42a and 42b of the first brake circuit can be opened and the total brake pressure in the corresponding brake cylinders of the wheel 32a and 32b is regulated in correspondence with the desire for braking that is reduced. The volume of brake fluid coming from at least one brake cylinder of the wheel 32a and 32b can be transferred back to the brake fluid reservoir 12 by at least one of the wheel's discharge valves 42a or 42v. Other activation strategies can also be carried out for the active regulation of the brake pressures in the two brake cylinders of the wheel 32a and 32b of the first brake circuit 26. Instead of a regulation of the brake pressure in the brake cylinders of the wheel 32a and 32b by means of activation AP- of the discharge valves of the wheel 42a and 42b, a pressure control can also be carried out

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using the first pressure sensor 84 or at least one pressure sensor in a wheel associated with the brake cylinders of the wheel 32a or 32b.

After the displacement of the predetermined accumulation volume towards the accumulation chamber 20, the constitution of pressure in the second brake circuit 28 can take place in a conventional manner and independently of the total brake pressure of the two brake cylinders of the wheel 32a and 32b of the first brake circuit 26, as! as can be modulated by the driver. Similarly, active pressure constitutions can also be made without actuation of the braking actuation element 14 through the conductor, in a conventional manner, through an opening of the main selector valve 90 in the second brake circuit 28.

It should be noted that the procedure described in the previous paragraphs to maintain a deceleration of the desired vehicle, predetermined by the driver, can also be performed without a generator activation.

Figure 2 shows a circuit diagram of a second embodiment of the braking system.

The braking system shown in Figure 2 differs from the embodiment described above in the fact that a braking system equipment with a accumulation chamber is used as a brake fluid accumulation device. Instead, the first valve 18, via a line 46 and the branch point 152 on line 74, is connected to the brake fluid reservoir 12.

The first valve 18 opens, as! as a hydraulic connection between the main brake cylinder 10 and the brake fluid reservoir 12 closes. Thus, after opening the first valve 18, there is the possibility of transferring the volume of brake fluid displaced in In the case of an adjustment of the floating piston of the main brake cylinder in an adjustment path below the adjustment path, it corresponds to the brake fluid reservoir 12, from the main brake cylinder 10, to the brake fluid reservoir 12 , without back pressure. After the opening of the first valve 18, therefore, the inward adjustment of the floating piston of the main brake cylinder in the adjustment travel below the limit travel path does not cause a braking effect of a brake cylinder of the wheel 32a, 32b, 86a or 86b. On the other hand, if the first valve 18 is closed, then an actuation of the floating piston of the main brake cylinder / of the braking actuation element 14 causes directly and without idle travel an increase in the braking pressure at least in the cylinders of wheel brake 86a and 86b. Also, the embodiment represented in this case thus enables a variable regulation of the idle path with the advantages already described, in particular with the advantageous use capacity of the braking device in the case of a suppression of a braking torque of the generator.

Figures 3 and 4 respectively show a circuit diagram of a third and fourth ways of executing the braking system.

The embodiments shown in Figures 3 and 4, in comparison with the braking systems described above, do not have a brake booster. Preferably, the braking systems described here are used in a vehicle, so that by means of the brake cylinder of the wheel 32a and 32b of the first braking circuit 26 the wheels arranged in the front axle of the vehicle can be braked. The above-mentioned advantages are guaranteed above all in the case of a use of this class of braking systems.

In this way, the driver has the possibility of braking without brake booster on the rear axle, thereby obtaining an advantageous braking sensation (pedal sensation). The constitution of pressure on the anterior axis can take place actively, where preferably, automatically, an amplification of the driver's braking desire is performed which represents a simplification for the driver in terms of force. In addition, such systems, also in the event that vacuum is not available, have the advantages of an adjustable distribution of the braking force.

Compared to a braking system according to the standard, all the braking systems described above additionally guarantee the advantage that, due to the rapid detection of a driver's braking desire by the sensor 17, the desire can already be reacted early to the desire of braking of the driver.

Figure 5 shows a flow chart to represent an embodiment of a method for operating a braking system of a vehicle, which is not contemplated within the present invention.

The method depicted in Figure 5 can be executed with a braking system with a main brake cylinder with a floating piston of the main brake cylinder that can be adjusted at least partially in the main brake cylinder and with an accumulation device of brake fluid to which a predetermined accumulation volume of a brake fluid can be transferred without back pressure. It should be noted that the possibility of executing the method is not limited to the braking systems described above.

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In a step of method S1 that can be optionally executed, an internal pressure is increased in the main brake cylinder by adjusting the floating piston of the main brake cylinder partially in the main brake cylinder in an adjustment path below a adjustment path corresponds to the accumulation volume. This happens through the closure of a first valve that can be controlled electrically, by means of which the brake fluid accumulation device is hydraulically connected to the main brake cylinder. Optionally, along with the step of method S1, a step of method S2 is also executed, where a second valve, by means of which a brake circuit of the braking system with at least one wheel brake cylinder is connected Hydraulically with the main brake cylinder, it is controlled in a mode at least partially open.

Optionally, instead of the method steps described above, a step of the method S3 can also be executed, where an increase in the internal pressure in the main brake cylinder is prevented by adjusting the floating piston of the main brake cylinder in The adjustment travel below the adjustment travel is limited, through an at least partial opening of the first valve. It is thus ensured that a volume of brake fluid smaller than the predetermined accumulation volume is transferred without back pressure from the main brake cylinder, by means of the first valve at least partially open, to the brake fluid accumulation device. Preferably, together with the step of method S3, also at least when the first valve is opened (completely), the second valve is controlled in a closed mode (step of method 4).

In addition to this, after the closure of the second valve, a volume of brake fluid can be pumped from a brake fluid reservoir to at least one brake cylinder of the brake circuit wheel (method step S41). Alternatively or complementary with respect to the passage of method S41, in a step of method S42, also at least one valve that can be adjusted continuously, of the brake circuit, by means of which at least one wheel brake cylinder is It is hydraulically connected to the brake fluid reservoir, it can be opened. In this way, a brake fluid displacement can be made from at least one wheel brake cylinder to the brake fluid reservoir. By the steps of method S41 and S42, the braking pressure in at least one brake cylinder of the brake circuit wheel can be actively regulated.

Preferably, in the step of method S42, only one valve that is continuously adjustable by a first wheel discharge valve and a second wheel discharge valve of the brake circuit is opened at least partially. the displacement of the brake fluid from a first brake cylinder of the wheel or from a second brake cylinder of the brake circuit wheel towards the brake fluid reservoir. For example, if one of the two inlet valves of the brake circuit wheel must be closed / kept closed due to an ABS regulation on the associated wheel, then the pressure regulation can take place by means of the wheel discharge valve associated to the other wheel of the common axis. Therefore, the functionality of the pressure regulation that can be controlled can optionally be performed with a wheel discharge valve of the two wheel discharge valves of a common axle. In this way, the complete elimination of a braking can also be carried out, if necessary. In this way, the method described here can be combined with traditional ABS regulation.

Claims (3)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. Braking system for a vehicle with a main brake cylinder (10), with a fixing piston of the main brake cylinder which can be adjusted at least partially in the main brake cylinder (10); a brake fluid accumulation device (12, 20) into which a predetermined volume of brake fluid can be transferred, where the brake fluid accumulation device (12, 20) is a fluid reservoir of brakes (12) or a low pressure accumulation chamber (20); a first valve (18) closed without power, which is hydraulically connected to the main brake cylinder (10) by a first supply line (44), and by means of which the brake fluid accumulation device (12, 20 ) is hydraulically connected to the main brake cylinder (10), so that in the case of an adjustment of the floating piston partially inside the main brake cylinder (10) in an adjustment path below a corresponding limit adjustment path at the accumulation volume, a volume of brake fluid that is smaller than the predetermined accumulation volume can be transferred from the main brake cylinder (10) to the brake fluid accumulation device (12, 20) by the first valve (18) at least partially open; a first brake circuit (26) with two wheel brake cylinders (32a, 32b) and in each case a wheel intake valve (54a, 54b) and in each case a wheel discharge valve (42a , 42b) per wheel brake cylinder (32a, 32b), where each of the two wheel intake valves (54a, 54b) and the two wheel discharge valves (42a, 42b) of the first brake circuit (26) has two connections and in each case it is a valve that can be adjusted continuously; a second valve (30) open without current, which, by means of a branch point (48) on the first supply line (44) is hydraulically connected to the main brake cylinder (10) and by which the first circuit of brakes (26) is hydraulically connected to the main brake cylinder (10), so that by means of the second closed valve (30) an increase in pressure can be prevented in the two brake cylinders of the wheel (32a, 32b) of the first brake circuit (26) in the case of the pressure increase in the main brake cylinder (10), and by the second valve (30) closed at least partially a pressure increase in the two brake cylinders of the wheel (32a, 32b) of the first brake circuit (26) can be transferred in the case of increased pressure in the main brake cylinder (10); a second brake circuit (28) with two wheel brake cylinders (86a, 86b), a switching valve (96), a high pressure selector valve (90), and in each case an intake valve of the wheel (108a, 108b) and in each case a wheel discharge valve (120a, 120b) per wheel brake cylinder (86a, 86b), where each of the two wheel intake valves (54a, 54b) of the second brake circuit (28) has two connections and in each case it is a valve that can be adjusted continuously, and each of the two wheel discharge valves (42a, 42b) of the second brake circuit ( 28) it has two connections and in each case it is a selector valve, where the second brake circuit (28), by means of a second supply line (88) leading to the high pressure selector valve (90), is hydraulically connected to the main brake cylinder (10), and where the switching valve (96), by means of a branching point (92) formed in the second power line (88), it is also hydraulically connected to the main brake cylinder (10); Y a control device (34), by which each of the two wheel intake valves (54a, 54b) and the two wheel discharge valves (42a, 42b) of the first brake circuit (can be controlled) 26), each of the two wheel intake valves (54a, 54b) and the two wheel discharge valves (42a, 42b) of the second brake circuit (28), the switching valve (96) and the high pressure selector valve (96), and additionally the first valve (18) and the second valve (30) can be switched in opposition, so that through a control of the first valve (18) in its open state and of the second valve (30) in its closed state the braking system can be controlled in a first mode, where an increase in pressure in the main brake cylinder (10) is prevented in the case of adjusting the floating piston of the Main brake cylinder partially in the main brake cylinder (10) in the adjustment travel below The adjustment path limits, and through a control of the first valve (18) in its closed state and the second valve (30) in its open state the braking system can be controlled in a second mode, where an increase in Pressure in the main brake cylinder (10) is guaranteed by adjusting the floating piston of the main brake cylinder, partially in the main brake cylinder (10), in the adjustment path below the adjustment path limits, characterized because, through the control of the first valve (18) in its open state and the second valve (30) in its closed state, an intervention of the main brake cylinder (10) in the two wheel brake cylinders (32a) is prevented , 32b) of the first brake circuit (26) and an increase in pressure in the two brake cylinders of the wheel (32a, 32b) of the first brake circuit (26) despite an increase in pressure in the brake cylinder main due to the 5 second valve (30) closed; through the control of the first valve (18) in its closed state and the second valve (30) in its open state an increase in pressure in the main brake cylinder (10), by means of the second valve (30) at least partially open, it can be transmitted to the two wheel brake cylinders (32a, 32b) of the first brake circuit (26); Y The braking system has exactly twelve valves that can be activated (18, 30, 42a, 42b, 54a, 54b, 10 90, 96, 108a, 108b, 120a, 120b) as the first valve (18), the second valve ( 30), the two intake valves of the wheel (54a, 54b) and the two wheel discharge valves (42a, 42b) of the first brake circuit (26), the two wheel intake valves (54a, 54b) and the two discharge valves (42a, 42b) of the second brake circuit (28), the switching valve (96) and the high pressure selector valve (90), which can be controlled at least in its open state and in its closed state by at least an electrical control signal (36) 15 provided by the control device (34), where the first valve (18) in its open state and the second valve (30) in its closed state can be switched in opposition through a signal of common current of the control device (34) as control signal (36). 2. Braking system according to claim 1, wherein the first brake circuit (26) comprises a pump (38), by means of which another volume of brake fluid can be pumped into the two brake cylinders of the wheel 20 (32a, 32b) of the first brake circuit (26) from the brake fluid reservoir that is used as a brake device. accumulation of brake fluid (12, 20) or from an additional brake fluid reservoir (12). 3. Braking system according to claim 2, wherein the braking system comprises an overpressure valve (76) disposed between a transport side of the pump (38) and the brake fluid reservoir (12).